diff --git a/app/src/main/java/io/github/wulkanowy/WulkanowyApp.kt b/app/src/main/java/io/github/wulkanowy/WulkanowyApp.kt
index 90b3581c8..eee70891e 100644
--- a/app/src/main/java/io/github/wulkanowy/WulkanowyApp.kt
+++ b/app/src/main/java/io/github/wulkanowy/WulkanowyApp.kt
@@ -11,6 +11,8 @@ import dagger.android.AndroidInjector
 import dagger.android.support.DaggerApplication
 import eu.davidea.flexibleadapter.FlexibleAdapter
 import eu.davidea.flexibleadapter.utils.Log
+import io.github.wulkanowy.data.db.SharedPrefProvider
+import io.github.wulkanowy.data.db.SharedPrefProvider.Companion.APP_VERSION_CODE_KEY
 import io.github.wulkanowy.di.DaggerAppComponent
 import io.github.wulkanowy.services.sync.SyncWorkerFactory
 import io.github.wulkanowy.ui.base.ThemeManager
@@ -33,6 +35,9 @@ class WulkanowyApp : DaggerApplication(), Configuration.Provider {
     @Inject
     lateinit var themeManager: ThemeManager
 
+    @Inject
+    lateinit var sharedPrefProvider: SharedPrefProvider
+
     @Inject
     lateinit var appInfo: AppInfo
 
@@ -47,6 +52,7 @@ class WulkanowyApp : DaggerApplication(), Configuration.Provider {
         RxJavaPlugins.setErrorHandler(::onError)
         Lingver.init(this)
         themeManager.applyDefaultTheme()
+        migrateSharedPreferences()
 
         initLogging()
         initCrashlytics(this, appInfo)
@@ -62,6 +68,13 @@ class WulkanowyApp : DaggerApplication(), Configuration.Provider {
         registerActivityLifecycleCallbacks(ActivityLifecycleLogger())
     }
 
+    private fun migrateSharedPreferences() {
+        if (sharedPrefProvider.getLong(APP_VERSION_CODE_KEY, -1) < 48) { // #596
+            sharedPrefProvider.delete(getString(R.string.pref_key_grade_modifier_plus))
+            sharedPrefProvider.delete(getString(R.string.pref_key_grade_modifier_minus))
+        }
+    }
+
     private fun onError(error: Throwable) {
         //RxJava's too deep stack traces may cause SOE on older android devices
         val cause = error.cause
diff --git a/app/src/main/java/io/github/wulkanowy/data/db/SharedPrefProvider.kt b/app/src/main/java/io/github/wulkanowy/data/db/SharedPrefProvider.kt
index a6d0a067e..6a9533959 100644
--- a/app/src/main/java/io/github/wulkanowy/data/db/SharedPrefProvider.kt
+++ b/app/src/main/java/io/github/wulkanowy/data/db/SharedPrefProvider.kt
@@ -8,6 +8,10 @@ import javax.inject.Singleton
 @Singleton
 class SharedPrefProvider @Inject constructor(private val sharedPref: SharedPreferences) {
 
+    companion object {
+        const val APP_VERSION_CODE_KEY = "app_version_code"
+    }
+
     fun putLong(key: String, value: Long, sync: Boolean = false) {
         sharedPref.edit(sync) { putLong(key, value) }
     }
diff --git a/app/src/main/java/io/github/wulkanowy/services/sync/SyncManager.kt b/app/src/main/java/io/github/wulkanowy/services/sync/SyncManager.kt
index 98fc35228..6b0469773 100644
--- a/app/src/main/java/io/github/wulkanowy/services/sync/SyncManager.kt
+++ b/app/src/main/java/io/github/wulkanowy/services/sync/SyncManager.kt
@@ -11,6 +11,7 @@ import androidx.work.NetworkType.UNMETERED
 import androidx.work.PeriodicWorkRequestBuilder
 import androidx.work.WorkManager
 import io.github.wulkanowy.data.db.SharedPrefProvider
+import io.github.wulkanowy.data.db.SharedPrefProvider.Companion.APP_VERSION_CODE_KEY
 import io.github.wulkanowy.data.repositories.preferences.PreferencesRepository
 import io.github.wulkanowy.services.sync.channels.DebugChannel
 import io.github.wulkanowy.services.sync.channels.NewEntriesChannel
@@ -32,10 +33,6 @@ class SyncManager @Inject constructor(
     appInfo: AppInfo
 ) {
 
-    companion object {
-        private const val APP_VERSION_CODE_KEY = "app_version_code"
-    }
-
     init {
         if (now().isHolidays) stopSyncWorker()
 
diff --git a/app/src/main/java/io/github/wulkanowy/utils/GradeExtension.kt b/app/src/main/java/io/github/wulkanowy/utils/GradeExtension.kt
index c863b030f..22dbc22f5 100644
--- a/app/src/main/java/io/github/wulkanowy/utils/GradeExtension.kt
+++ b/app/src/main/java/io/github/wulkanowy/utils/GradeExtension.kt
@@ -67,8 +67,8 @@ inline val Grade.colorStringId: Int
 
 fun Grade.changeModifier(plusModifier: Double, minusModifier: Double): Grade {
     return when {
-        modifier != .0 && plusModifier != .0 && modifier > 0 -> copy(modifier = plusModifier)
-        modifier != .0 && minusModifier != .0 && modifier < 0 -> copy(modifier = -minusModifier)
+        modifier > 0 -> copy(modifier = plusModifier)
+        modifier < 0 -> copy(modifier = -minusModifier)
         else -> this
     }
 }
diff --git a/app/src/main/res/values-pl/preferences_values.xml b/app/src/main/res/values-pl/preferences_values.xml
index facec3f0b..94cdbcdde 100644
--- a/app/src/main/res/values-pl/preferences_values.xml
+++ b/app/src/main/res/values-pl/preferences_values.xml
@@ -23,7 +23,7 @@
     </string-array>
 
     <string-array name="grade_modifier_entries">
-        <item>Domyślna</item>
+        <item>0,0</item>
         <item>0,25</item>
         <item>0,33</item>
         <item>0,5</item>
diff --git a/app/src/main/res/values/preferences_defaults.xml b/app/src/main/res/values/preferences_defaults.xml
index 733d71b0c..91b357d93 100644
--- a/app/src/main/res/values/preferences_defaults.xml
+++ b/app/src/main/res/values/preferences_defaults.xml
@@ -13,7 +13,7 @@
     <bool name="pref_default_services_wifi_only">false</bool>
     <bool name="pref_default_notifications_enable">true</bool>
     <bool name="pref_default_notification_debug">false</bool>
-    <string name="pref_default_grade_modifier_plus">0.0</string>
-    <string name="pref_default_grade_modifier_minus">0.0</string>
+    <string name="pref_default_grade_modifier_plus">0.33</string>
+    <string name="pref_default_grade_modifier_minus">0.33</string>
     <bool name="pref_default_fill_message_content">true</bool>
 </resources>
diff --git a/app/src/main/res/values/preferences_values.xml b/app/src/main/res/values/preferences_values.xml
index 52de39e1b..3d2cf1654 100644
--- a/app/src/main/res/values/preferences_values.xml
+++ b/app/src/main/res/values/preferences_values.xml
@@ -55,7 +55,7 @@
     </string-array>
 
     <string-array name="grade_modifier_entries">
-        <item>Default</item>
+        <item>0,00</item>
         <item>0,25</item>
         <item>0,33</item>
         <item>0,5</item>
diff --git a/app/src/test/java/io/github/wulkanowy/utils/GradeExtensionTest.kt b/app/src/test/java/io/github/wulkanowy/utils/GradeExtensionTest.kt
index 31618fd4f..2bba619f0 100644
--- a/app/src/test/java/io/github/wulkanowy/utils/GradeExtensionTest.kt
+++ b/app/src/test/java/io/github/wulkanowy/utils/GradeExtensionTest.kt
@@ -41,9 +41,9 @@ class GradeExtensionTest {
     }
 
     @Test
-    fun changeModifier_default() {
-        assertEquals(.33, createGrade(5, .0, .33).changeModifier(.0, .0).modifier, .0)
-        assertEquals(-.33, createGrade(5, .0, -.33).changeModifier(.0, .0).modifier, .0)
+    fun changeModifier_zero() {
+        assertEquals(.0, createGrade(5, .0, .5).changeModifier(.0, .0).modifier, .0)
+        assertEquals(.0, createGrade(5, .0, -.5).changeModifier(.0, .0).modifier, .0)
     }
 
     @Test